Assessment of materials for accelerator applications using proton irradiation

An understanding of material response to the severe conditions of a spallation neutron environment is lacking. Proton irradiation has proven to be an extremely effective tool in emulating the effects of neutron irradiation in austenitic stainless steels and may be able to provide a means of obtaining a first look at the irradiation performance of candidate alloys in preparation of irradiation campaigns in more prototypic environments. This work focuses on the ferritic-martenisitc candidate steel, T-91. Samples in the form 20 mm × 2 mm × 1 mm were irradiated with 2.0 MeV protons to doses of 3, 7 and 10 dpa at a dose rate of 2 × 10^-5 dpa/s and a temperature of 450°C. Samples were irradiated in both the as-received and He pre-implanted (to 100 appm) conditions. The microstructure of irradiated samples was examined using a JEOL2000FX. Dislocation loop size and number density were determined by imaging loops using the brightfield technique and irradiation hardening was measured by Microhardness indentation. Results show that the irradiated microstructure consists of a moderate density (5 × 10²¹ m ^-3) of 10-15 nm dislocation loops and that no voids or second phases are formed during irradiation. The hardness increases by 95 kg/mm² or 280 MPa after a dose of 10 dpa. He implantation to 100 appm does not significantly alter either the microstructure or the hardening following irradiation.